The present invention relates to a modifier composition for methacrylate resin, which is used for a thermoplastic resin particularly for a methacrylate resin and can stably give an molding article having an excellent strength (impact resistance) without deteriorating transparency, color tone and appearance thereof under a wide range of injection molding conditions.
A methacrylate resin has been used in lighting devices and outdoor article due to its high transparency and good weatherability. On the other hand, its strength is not necessarily sufficient, and thus various kinds of impact modifiers have been attempted to be added thereto. For example, Japanese Examined Patent Publication Nos. 55-27576 (1980) and 62-230841 (1987) disclosed modifying technique relating thereto. It is necessary not to lose transparency, color tone and appearance of a methacrylate resin under a wide range of processing conditions. However, when the techniques previously disclosed are used in processing a methacrylate resin, it is difficult to satisfy the requirement that a methacrylate resin excellent in strength is stably obtained without deteriorating transparency, color tone and appearance thereof under a wide range of processing conditions. In fact, a transparent molded articles can be obtained under limited processing conditions, and an appearance thereof becomes worse due to agglomeration of the impact modifier during processing. Namely, if a molding temperature is raised in order to obtain a molded article having high transparency, the article is thermally deteriorated, color tone thereof becomes lower, and a resin gets yellowish under a slight fluctuation in processing conditions. On the other hand, if the injection molding temperature is set low, appearance of the article becomes worse so that transparency thereof is deteriorated significantly.
As a measure for these problems, some investigations have been carried out in order to stably obtain a molded article having high physical properties. For example, there are disclosed a method for using a methacrylate resin having a broad distribution of molecular weight to improve fluidity and the balance between strength and fluidity (Japanese Examined Patent Publication No. 1-29218 (1989)), and a technique for mixing an impact modifier with a dispersing agent in the state of latex to prevent agglomeration of the impact modifier as a means for reducing the so-called fish eye on the surface of an injection molding (Japanese Examined Patent Publication No. 2-2358 (1990)). However, these were not sufficient from the viewpoint that a molded article having excellent strength is obtained without deteriorating transparency, color tone and appearance thereof under a wide range of injection molding conditions in the present invention.
In the present invention there is provided a modifier composition for a methacrylate resin, which can stably give a molded article excellent in strength without deteriorating transparency, color tone and appearance thereof under a wide range of injection molding conditions.
In view of these circumstances, the present inventors extensively studied a resin composition having an excellent strength without deteriorating characteristics of a methacrylate resin, namely, transparency, color tone and appearance under a wide range of injection molding conditions. As a result, it was found out that the above problems in injection molding can be solved by blending an impact modifier, a polymer processing aid and a reducing compound with a methacrylate resin to complete the present invention.
Namely, the present invention relates to
(1) a modifier composition for a methacrylate resin comprising an impact modifier, a polymer processing aid and a reducing compound, wherein a ratio of the impact modifier to the polymer processing aid is 95/5 to 80/20 in weight, and an amount of the reducing compound is 0.25 to 1.25 parts by weight based on 100 parts by weight of the total amount of the impact modifier and the processing aid,
(2) the modifier composition for a methacrylate resin of the above (1), wherein the impact modifier is obtained by polymerizing a monomer mixture comprising (meth)acrylate and an aromatic vinyl monomer in the presence of an acrylic rubber and/or a conjugated diene rubber,
(3) the modifier composition for a methacrylate resin of the above (1) or (2), wherein the polymer processing aid comprising 50 to 70% by weight of methyl methacrylate and 30 to 50% by weight of the other monomer copolymerizable therewith,
(4) the modifier composition for a methacrylate resin of the above (1), (2) or (3), wherein a specific viscosity of the polymer processing aid is 2.5 to 5.0 regarding to 0.4% by weight of a toluene solution at 30xc2x0 C.,
(5) the modifier composition for a methacrylate resin of the above (1), (2), (3) or (4), wherein the reducing compound is a compound containing sulfur and/or phosphorus, and
(6) the modifier composition for a methacrylate resin of the above (5),
wherein the reducing compound is an organic reducing compound.
In the present invention there is no particular limitation for a methacrylate resin, it includes a resin containing at least 50% by weight of methacrylate unit, preferably at least 50% by weight of methyl methacrylate unit, and any commercially available methyl methacrylate resins can be used.
There is no particular limitation for an impact modifier used in the present invention, as long as it can be used in a methacrylate resin. In particular, the modifier is preferable which is prepared by polymerizing a monomer mixture comprising (meth)acrylate and an aromatic vinyl monomer, to which another copolymerizable monomer may be added depending on the object, in the presence of an acrylic rubber and/or a conjugated diene rubber. Since these are well-compatible with a methacrylate resin to significantly improve impact strength thereof As these modifiers, there are known those having various kinds of multilayer structure, and, for example, those disclosed in Japanese Examined Patent Publication No. 55-27576 (1980) can also be used. Further, the polymerization method is not particularly limited, but the known emulsion polymerization method is practically convenient. However, if only the impact modifier is added to a methacrylate resin, there arises the problem that transparency, color tone and appearance inherent in a methacrylate resin are deteriorated depending on processing conditions.
As a conjugated diene rubber, examples are those rubbers comprising diene monomers such as butadiene, isoprene and chloroprene. As an acrylic rubber, examples are alkyl acrylates having 1 to 12 carbon atoms in the alkyl group, such as ethyl acrylate, n-butyl acrylate, n-octyl acrylate and 2-ethylhexyl acrylate. Examples of an aromatic vinyl monomer are styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, xcex1-methylstyrene and chlorostyrene. Examples of a (meth)acrylate are methyl acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate, hexyl(meth)acrylate, cyclohexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, isobomyl(meth)acrylate, phenyl(meth)acrylate and benzyl(meth)acrylate, and the like.
The polymer processing aid used in the present invention should have a relatively high molecular weight, and it is effective to use the modifier having a several to tens times higher molecular weight than that of a generally used methacrylate resin (weight average molecular weight is about 100,000). That is, apart from the generally conceivable technical idea in the prior art, the addition of a small amount of the polymer processing aid reduces the dependence of transparency on processing conditions, although the viscosity in the system rises slightly. The technical reason speculated for this is that the melting elasticity in the system becomes high to improve inferior appearance and stabilize transparency. Further, an amount of the polymer processing aid in the present invention is preferably 50 to 70% by weight of methyl methacrylate in view of compatibility with matrix. If the amount is less than 50% by weight, transparency decreases due to deviation from refractive index of matrix. If the amount of methyl methacrylate is more than 70% by weight, its compatibility with matrix is lowered due to increased rigidity of molecule in addition to relatively high molecular weight, and thereby transparency becomes low adversely. The above-mentioned methyl methacrylate is preferably copolymerized with a softening component. For example, the methyl methacrylate is preferably obtained by copolymerizing 50 to 70% by weight of methyl methacrylate with 30 to 50% by weight of the other copolymerizable monomers. The other copolymerizable monomer is preferably (meth)acrylates having one to eight carbon atoms in the alkyl group other than methyl methacrylate. If necessary, 30% by weight of the (meth)acrylates may be replaced by the other copolymerizable monomers such as styrene and acrylonitrile. Namely, (meth)acrylate monomers are preferable as the softening component without losing weatherability of the methacrylate resin. Examples of the softening component are butyl methacrylate, ethyl acrylate, butyl acrylate, octyl acrylate and 2-ethylhexyl acrylate, which are preferably used in view of costs and the like. As a matter of course, the refractive index of the polymer processing aid should be adjusted to that of a methacrylate resin as much as possible without losing transparency of the obtained molded article. In addition, the molecular weight of the polymer processing aid should be relatively high as described above. That is, its molecular weight is preferably 2.5 to 5.0 in terms of specific viscosity (xcex7sp), more preferably 2.5 to 4.0. If the molecular weight of the methacrylate resin is less than 2.5 in specific viscosity, there is no modifying effect on the object of the present invention. On the other hand, if it is more than 5.0, the compatibility with the matrix resin is deteriorated to significantly lower transparency. Here, the conditions for measuring the specific viscosity xcex7sp are as follows: That is, the sample is dissolved at a concentration of 0.4% by weight in toluene and the viscosity xcex7sp is obtained by using a viscometer at 30xc2x0 C. according to the equation xcex7sp=(xcex7xe2x88x92xcex70)/xcex70. In this equation, xcex7 is the viscosity of the solution and xcex70 is the viscosity of the solvent (toluene).
A ratio of the impact modifier to the polymer processing aid in weight is 95/5 to 80/20. If the ratio of the polymer processing aid to the impact modifier is more than 95/5, the effect improving the above-mentioned object is small. On the other hand, if the ratio is less than 80/20, the effect of improving impact resistance becomes low in spite of the amount of the impact modifier, and the transparency is also lowered. That is, it is estimated that compatibility of the polymer processing aid with a methacrylate resin as the object is lowered due to relatively high molecular weight of the polymer processing aid, thus transparency decreases adversely. As the polymer processing aid, any products commercially available can be used as long as they satisfy the conditions described above. However, if only the impact modifier and the polymer processing aid are added to a methacrylate resin, a resin having high transparency and high impact strength is obtained, and transparency thereof is improved but color tone is not improved at all.
Finally, the reducing compound in the present invention is a substance which exhibits so-called reductive actions such as peroxide decomposition, deoxygenation and hydrogenation on the subject substance of oxidization by oxidative actions such as oxidation and dehydrogenation for the substance. In particular, it is preferable to use compounds with a structure containing sulfur and/or phosphorus. Example thereof are a reducing organic compound containing phosphor such as hypophosphorous or its derivatives, phosphorous acid or its derivatives, and a reducing organic compound containing sulfur such as thiol, thioether and sulfoxide. Among these compounds having a structure containing sulfur and/or phosphorus, the reducing compound having a chemical structure containing phosphorus includes antioxidants such as the trade names of PEP-4C, PEP-8, PEP-8F, PEP-8W, PEP-11C, PEP-24G, PEP-36, HP-10, 2112, 260, 522A, 329K, 1178, 1500, C, 135A, 3010, and TPP, which are commercially available from Asahi Denka Kogyo K. K. The reducing compound having a chemical structure containing sulfur includes antioxidants such as the trade names of Irganox PS800 and Irganox PS802 FL, which are available from Chiba Geigy.
Thermal degradation at molding can be drastically improved by using the reducing compound in combination with the impact modifier and the polymer processing aid. And thereby a molding article having superior impact strength can be obtained without deteriorating transparency, color tone and appearance thereof under a wide range of injection molding conditions.
An amount of the reducing compound is 0.25 to 1.25 parts by weight based on 100 parts by weight of the total amount of the impact modifier and the polymer processing aid. If the amount is less than 0.25 part by weight, the improving effect of the stabilizer is low. On the other hand, if the amount is more than 1.25 parts by weight, color tone is contrarily deteriorated.
There is no particular limitation for a method of mixing the impact modifier, the polymer processing aid and the reducing compound. There can be used a method of mutually mixing a mixture thereof in the state of powder with a methacrylate resin, or the impact modifier, and a method of mixing the impact modifier, the polymer processing aid and the reducing compound, which are obtained by polymerization, in the state of latex, and then mixing them powdered in a usual manner (agglomeration, washing with water, filtration, drying) with the methacrylate resin to be modified. The reducing compound may also be added during the polymerization process of the impact modifier.
The modifier composition of the present invention is suitably applied to a thermoplastic resin, particularly a methacrylate resin. An amount thereof is 5 to 50 parts by weight based on 100 parts by weight of the methacrylate resin. If the amount is less than 5 parts by weight, there is no effect of improving impact strength. On the other hand, if the amount is more than 50 parts by weight, transparency decreases.